The chilling accusation by Malaysia that the assassins who killed Kim Jong-nam, the half-brother of the North Korean dictator Kim Jong-un, used the world’s most powerful chemical toxin has set off a global shockwave well beyond Asia. Malaysian authorities are convinced that a North Korean hit squad — one member an accredited diplomat — was behind the attack on Feb. 13, 2017, in Malaysia’s largest international airport near the capital, Kuala Lumpur, and that several of them have fled the country. But those announced findings still leave questions.

Why or how did the two young women now in custody who carried out the attack, smearing VX toxin on Kim Jong-nam’s face, say Malaysian police, survive? Were they inoculated prophylactically with an antitoxin? But what about all the people milling around the departure area of the airport, in particular at least one person who tried to help the stricken man, as well as the airport officials and medical team who attempted to treat him as he collapsed, soon to die on the way to a hospital? Authorities closed the airport to decontaminate it, but by then many people could have been exposed.

Finally, what international organization is in a position to deal with the closed North Korean regime, which demonstrated so coldly and publicly what amounts to a form of chemical warfare in a civilian setting that could be used by others? When members of a Japanese sect sprayed the toxic sarin in a Tokyo subway in 1995, killing 12 people, the government declared it an act of domestic terrorism. North Korea, which is not only accumulating a nuclear arsenal but also has a history of assassinations, kidnappings and massacres beyond its borders, now appears to be willing to use toxic chemicals on an international stage.

In this fourth installment of an occasional series on research and data useful to readers, PassBlue takes a look at the international convention banning the use of chemical weapons, which came into force in 1997, after years of negotiations. The Chemical Weapons Convention is managed by the Organization for the Prohibition of Chemical Weapons, or OPCW, based in The Hague, through a working agreement with the United Nations,

Around the world, 192 countries have signed the convention, pledging to destroy any weapons in their possession and — as in the case of Syria most recently — the precursor ingredients assembled to create toxic chemicals as well as the means of production. The organization monitors compliance. For a list of its members, see www.opcw.org.

North Korea has not signed the treaty (and neither has Israel nor Egypt, though bizarrely, the Holy See has). As of Feb. 24, the OPCW was not part of the Malaysian investigation. Malaysia is often slow to bring in outside experts, though it has signed the convention.

The organization said in a statement: “According to media reports, the Malaysian authorities seem to have determined that the nerve agent VX was used in a killing at the airport on 13 February. Any use of chemical weapons is deeply disturbing. OPCW stands ready to provide its expertise and technical assistance, if required, to any State Party [country] to the Chemical Weapons Convention.”

The organization’s executive council will be holding a previously scheduled session from March 7 to 10, and the Malaysian case is likely to be discussed.

In explaining the evolution of thinking on what defines a chemical weapon and other information relevant to their production and use, the OPCW says that the traditional definition of a chemical weapon was once a bomb or a shell loaded with toxins.

It adds: “The Convention defines chemical weapons much more generally. The term chemical weapon is applied to any toxic chemical or its precursor that can cause death, injury, temporary incapacitation or sensory irritation through its chemical action. Munitions or other delivery devices designed to deliver chemical weapons, whether filled or unfilled, are also considered weapons themselves.

“The toxic chemicals that have been used as chemical weapons, or have been developed for use as chemical weapons, can be categorized as choking, blister, blood, or nerve agents.”

The most well-known agents are the following: choking agents — chlorine and phosgene; blister agents (or vesicants) — mustard and lewisite; blood agents — hydrogen cyanide; and nerve agents — sarin, soman, VX. VX is an oily liquid originally developed in Britain in the early 1950s as a potential pesticide.

For a comprehensive account of how definitions are determined and how monitoring must take into account that some elements that may be combined to make toxic weapons may in themselves have other benign uses, the OPCW provides explanations. A chart, below, delineating the types of weapons and how fast they can act is also included on this site.

In Washington, D.C., the Arms Control Association, a nongovernmental group, offers a useful chart comparing chemical and biological weapons, as well as other information on the Chemical Weapons Convention.

CW Agent Group, Persistency Rate of Action

Barbara Crossette

Barbara Crossette is the senior consulting editor and writer for PassBlue and the United Nations correspondent for The Nation. She is also a member of the Council on Foreign Relations. She has also contributed to the Oxford Handbook on the United Nations.

Previously, Crossette was the UN bureau chief for The New York Times from 1994 to 2001 and previously its chief correspondent in Southeast Asia and South Asia. She is the author of “So Close to Heaven: The Vanishing Buddhist Kingdoms of the Himalayas,” “The Great Hill Stations of Asia” and a Foreign Policy Association study, “India Changes Course,” in the Foreign Policy Association’s “Great Decisions 2015.”

Crossette won the George Polk award for her coverage in India of the assassination of Rajiv Gandhi in 1991 and the 2010 Shorenstein Prize for her writing on Asia.